Chick embryos can be "woken up" in the egg long before hatching by rousing them with the sound of clucking hens, a study has shown.
The findings may have important implications for premature babies, researchers believe.
"This work showed that embryo brains can function in a waking-like manner earlier than previously thought -- well before birth," said study leader Dr Evan Balaban, from McGill University in Montreal, Canada.
"Like adult brains, embryo brains also have neural circuitry that monitors the environment to selectively wake the brain up during important events."
Dr Balaban's team devised experiments in which brain activity in unhatched chick embryos was monitored using an advanced scanning technique.
The researchers found that during the final 20pc of life before hatching, the chicks displayed brain activity that mirrored being asleep or awake.
Prior to this point in development, embryos were in a state that was "neither like sleep nor waking", said Dr Balaban.